The document provides an overview of the human skeleton, detailing its functions such as support, protection, movement, blood formation, electrolyte balance, and acid-base balance. It explains the structure and classification of bones, joints, and muscles, describing their roles in the body, including various types of joints and muscle mechanisms. Additionally, it highlights interesting facts about bones, including their sizes, common injuries, and diseases.

1. Skeleton – Movement & Locomotion

2. Functions of Human Skeleton
Support
Bones of legs, pelvis, and vertebral column hold up the
body; the mandible supports the teeth; nearly all bones
provide support for muscles; many other soft organs are
directly or indirectly supported by nearby bones.
Protection
Bones enclose and protect the brain, spinal cord, lungs,
heart, pelvic viscera and bone marrow.
Movement
Skeletal muscle would serve no useful purpose if not for
the rigid attachment and leverage provided by bones. Leg
and arm movements are the most obvious examples; a less
obvious one is that ventilation of the lungs depends on
movement of the ribs by skeletal muscles.
Blood Formation
Red bone marrow is the major producer of blood cells,
including most cells of the immune system.
Electrolyte balance
The skeleton is the body’s main mineral reservoir. It stores
calcium and phosphate and releases them according to the
body’s physiological needs.
Acid-base Balance
Bone buffers the blood against excessive pH changes by
absorbing or releasing alkaline mineral salts.
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3. Parts of the Skeletal System
Bones (Skeleton)
Joints
Cartilages
Ligaments
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4. Bone
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Composition of Bone
When a bone is placed in weak HCl medium, the calcium
of bone slowly starts dissolve due to the action of acid
(2HCl + Ca -> CaCl2 + H2). Once the calcium is dissolved,
there is nothing to keep the bone hard – all that is left
is the soft bone tissue. With some effort and you can
really get the bone to bend.
If a bone is strongly heated its organic matter is
destroyed and only the mineral part will remain. Such a
bone turns brittle and quickly breaks.

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Classification of Bones
(On the basis of shape)

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Structure of a Long Bone
Diaphysis
Long central shaft.
Epiphysis
Rounded ends of long bones.
Epiphyseal Plates
Plates of cartilage, known as growth plates which allow growth
in length childhood.
Cancellous bone
Where blood cells are made.
Compact bone
Gives strength to the hollow part of the bone.
Periosteum
Ligaments and tendons attach to the periosteum.
Marrow cavity
Where white blood cells are made.

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Structure of a Long Bone

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Types of Bone Marrow
Red Bone Marrow Yellow Bone Marrow
Red colored (due to
erythrocytes), active vascular
tissue in the long bone.
Yellow colored (due to
predominance of adipocytes),
inactive vascular tissue in the
long bone.
Has few fat cells. Has more fat cells.
Produces blood corpuscles. Produces blood corpuscles in
emergencies.
During fetal life and at birth it
occurs throughout the
skeleton.
With age red bone marrow is
gradually replaced in the long
bones by yellow bone marrow.

9. It is composed of around 270 bones at birth – this total
decreases to around 206 bones by adulthood after some
bones get fused together.
The Human Skeleton
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Axial Skeleton Appendicular Skeleton
Each belongs to one of 2 large groups :
Forms long axis of the body.
Includes the bones of the
skull, vertebral column, and
rib cage.
These bones are involved in
protection, support, and
carrying other body parts.
Bones of upper & lower limbs
and the girdles (shoulder
bones and hip bones) that
attach them to the axial
skeleton.
Involved in locomotion and
manipulation of the
environment.

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Axial Skeleton
Skull (29)
Cranium (8) Face (14)
Hyoid (1) Ear Ossicles (6)

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Axial Skeleton
Vertebral Column [26(33)]
Vertebral column is curved to maintain balance of body in
an erect position. The curvature absorbs pressure and
shock while walking, running and protects the column from
breaking.

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Structure of a Typical Vertebrae
The main body of the vertebra is called as centrum.
Over the centrum is the neural arch that provides
protection to the spinal cord.
The neural arch bears ma median spinous process or the
neural spine to which muscles are attached.
Two transverse processes project laterally form the base
of the neural arch.
The transverse processes provide additional surface for
the attachment of muscles.
The articular facets provide surfaces for articulation with
the adjacent vertebrae.

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Different Types of Vertebrae

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Axial Skeleton
Rib Cage [Ribs (24) + Sternum (1)]

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Appendicular Skeleton
Fore Limbs (30×2 = 60)

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Appendicular Skeleton
Hind Limbs (30×2 = 60)

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Appendicular Skeleton
Girdles (6)
Pectoral Girdle (4)
Pelvic Girdle (2)

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Differences between Male &
Female Skeleton

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Joints
The point at which two separate bones meet is
called a joint.
Types of Joints :

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Types of Joints
Fibrous / Immoveable joints
The bones at an immoveable joint cannot move.
They overlap or interlock, and are held together by a tough
fiber.
E.g. The skull.
Cartilaginous / Slightly moveable joints
The bones at a slightly moveable joint can only move a little.
They are held together by strong straps called ligaments and
are joined by protective pads known as cartilage.
E.g. The ribs.

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Types of Joints
Synovial joint / Freely moveable joints
At a freely moveable joint the bones move freely.
They are also known as synovial joints, and are the largest
group of joints found in the body.
E.g. The hips, shoulders and knees.

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Structure of Synovial Joint
Synovial cavity is present in synovial joints.
Bones are covered by a layer of hyaline cartilage (articular
cartilage), which reduces the friction during movement.
Synovial joints are surrounded by the articular capsule,
which is composed of two layers: outer fibrous membrane
layer and the inner synovial membrane layer.
The fibrous membrane layer is composed of dense
irregular connective tissue which helps the bones from
dislocation during movement.
The fibers of the fibrous membrane in some joints form
ligaments which hold the bone together in joints.
Synovial membrane secretes the synovial fluids, which is a
viscous, pale yellow fluid, consisting of hyaluronic acid
(secreted by fibroblactic cells of synovial membrane),
interstitial fluid (filtered from blood) and phagocytic cells.
Hyaluronic acid acts as lubricating agent during movement
and interstitial fluid supplies nutrition and oxygen to
synovial cells as well as removes the carbon dioxide and
other waste products from bone cells. Phagocytic cells
remove the microbes and debris.
Bursae: Sac like structure (bursae) is present in some
synovial joints (knee and shoulder joints) to alleviate the
frictions.
Tendons: Synovial (tendon) sheaths (tube like bursae) are
also present to reduce frictions in some synovial joints
(shoulder, ankles, fingers, toe, wrists, ankle).

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Types of Synovial Joint
Joint Kind of motion Location in the
human body
Hinge Forward or
backward motion
Knees and Elbows
Bal and Socket Allows bones to
swing in the circles
Shoulders and Hips
Pivot One bone rotates
around another
Neck
Gliding One bone to slide
over another
Wrists and Ankles
Hinge Joint Ball & Socket Joint
Pivot Joint Gliding Joint

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Muscles
Most muscles are long bundles of contractile tissue. Each
muscle usually has two ends – a fixed end where the muscle
originates and a movable end which pulls some other parts.
This movable end is drawn out to form a tough structure the
tendon which is attached to the bone. When stimulated by the
nerve the muscle contracts to become shorter and thicker
and thus it pulls the bone at the movable end. Muscles can
only contract and relax, they cannot lengthen.
The muscles in the body provide the means of all
movements.
They cover the skeletal framework and also give
contour (shape) to the body.
Muscles help to maintain body pressure while
sitting, standing or walking.

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Antagonistic Muscles
Antagonistic Muscle Groups List
A muscle that opposes the action of another are a
ntagonistic muscles.

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Types of Muscles

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Lever Mechanism

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Levers in Human Skeleton
First order lever
E.g. The joint between the head and the first vertebra.
Second order lever
E.g. Found in the lower leg when someone stands on
tiptoes.

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Levers in Human Skeleton
Third order lever
E.g. Elbow joint.
Top 10 Fascinating Facts About Human Bones
1. Smallest Bone in the Human Body : Stirrup Bone.
2. Biggest (and Strongest) Bone in the Human Body : Femur.
3.Body Part with the Most Bones :The Hands.
4. Most Fragile Bone in the Body : TheToe Bones.
5. Most Commonly Broken Bone : The Ankle.
6. Most Common Form of Bone Surgery :Arthroscopic Surgery.
7. Most Common Bone Disease : Osteoporosis.
8. Most Common Forms of Bone Cancer : Osteosarcoma.
9.Weirdest Disease of the Human Bone : Disappearing Human Bone Disease.
10. Broke the Most Bones over a Lifetime : Evel Knievel.